1. Field of the Invention
The present invention relates to oscillating devices for electronic systems and more particularly relates to implementations of oscillating devices and to improved methods for reducing electromagnetic emissions of harmonic frequencies from electronic systems employing the oscillating devices therein.
2. The Prior Art
Almost every electronic equipment, device, appliance or system in use today uses at least one clocking source to synchronize the operation of all electronic components therein. Progress in computer and electronics technologies has demanded higher clocking frequency for faster operation speed and greater numbers of electronic circuits for more complex functionality. One side effect of the higher clock speeds and additional circuit elements has been increased unwanted electromagnetic emissions at various frequencies, especially at very high frequencies.
A clocking source generally comprises an oscillator circuit for converting a steady and direct current into a given waveform while maintaining the frequency of the waveform within stated limits. For example, sinusoidal oscillators generate sinusoidal waveforms, relaxation oscillators can generate rectangular pulses (square waves) and sawtooth and peaked waveforms. Electromagnetic emission is the transmission of energy in the form of conducted or radiated waves having both an electric and a magnetic component. The sources of electromagnetic radiation are accelerated electrical charges and oscillating currents, which all originate from the clocking source and other electronic components within the system.
It has been known for a long time that excessive electromagnetic emissions from an electronic system may illogically asynchronize operations of nearby electronic systems. Other deleterious effects of electromagnetic radiation have been proved problematic in many areas. Various regulations and organizations have been established to regulate and enforce established standards to control the electromagnetic emissions from the electronic systems. These measures place a tremendous pressure on manufacturers that design and manufacture electronic systems, all must be certified by the regulations before being released to marketplace.
There have been many efforts in the past years to reduce the electromagnetic emissions. One of the common solutions is to shield electronic systems using conductor materials. Other methods include adding radio frequency filters in data paths and employing multiple layered printed circuit boards. However, as the frequency of the clocking source gets higher, these methods become less effective and the cost of the shielding increases considerably. This has motivated a close look at the radiation source comprising the electronic components driven by the clock oscillators, and the clock oscillator itself that fundamentally produces the oscillating frequency.
One of the prior-art efforts is U.S. Pat. No. 5,430,392 to Matejic, which discloses a clock system and method for reducing the electromagnetic emissions of the clock frequency from an electronic system. From the perspective of employing a C.I.S.P.R quasi-peak detector to measure the electromagnetic emissions, Matejic discloses an approach of using a slower signal to vary the frequency of a clocking source over a "broad" frequency range (20% of nominal frequency in the only disclosed example) to spread the emission energy over the frequency range so that the C.I.S.P.R quasi-peak detector does not have enough time to charge at its measured frequency. This lowers the measured emissions from a device using the clock system.
A second example of the efforts of the prior art to reduce EMI from electronic equipment is U.S. Pat. No. 5,426,392 to Kornfeld. To reduce electromagnetic emissions from an electronic system that must be synchronized by a clock source, Kornfeld uses a noise source to add onto a pure frequency signal from a clocking source so as to generate a clocking signal whose phase is modulated by the noise source. With a band-pass filter placed just before the output of the clocking signal, the modulating phase can be tightly controlled and therefore spreads unwanted emissions within a small range surrounding the frequency of the pure clocking signal.
These aforementioned approaches and examples appear to resolve some of the problems of the electromagnetic radiation generated from clocking sources by introducing an additional source to modulate a high frequency clocking signal. However, none have demonstrated practical solutions to or satisfy current systems. For instance, in the Matejic method, a wide swing of the clock frequency is required to deactivate the quasi-peak detector in EMI measurement equipment to result in a lowered measured level. Most electronic equipment, however, would not work properly if the clock frequency were varied over a wide range. Both aforementioned methods have failed to address concerns of compatibility with the most widely used oscillating devices such as crystal resonators where there is no dedicated power input to energize the electronics required for those methods to work. Further these solutions have failed to address concerns of power consumption and physical fitting in aforementioned approaches and examples. There is, thus, a great need for a generic solution to a clocking source that can be used in any conventional electronic system, especially digital electronics systems, with no modifications therein.
Many systems, such as personal computers, are designed to respond to an idle mode in which the system is paused for an excessive period of time. There has been another need for a clocking source to respond to such idle mode so as to stop generating oscillating signals thereby idling the system to reduce the power consumption to a minimum. In order to recondition many electronic systems in use today that may potentially produce excessive electromagnetic radiation therefrom if the original condition thereof changes, there exists another need for a clocking source that is readily able to replace a conventional one and provide an improved clocking signal that would reduce electromagnetic radiation, be compatible with the power-down mode and work correctly as a clock source.
Accordingly, an important object of the present invention is to provide a generic clock generator signal device that will effectively spread the higher harmonic frequencies in electronic system so as to minimize their electromagnetic emissions while providing a usable clock signal to the system.
Another object of the invention is to provide an improved class of devices that is readily available to replace, and compatible in physical fitting and electrical operation to an existing oscillating device or element that would otherwise cause the electromagnetic emissions from a system centralized by the oscillating device.
Still another object of the invention is to have an improved signal device that works with existing oscillating devices to eliminate the potential of causing electromagnetic emissions.
Other objects, together with the forgoing are attained in the exercise of the invention in the following description and resulting in the embodiment illustrated in the accompanying drawings.